1. Field of the Invention
The present invention relates to a sensing method and device based on the surface plasmon resonance techniques, particularly to a sensing method using the electro-optical modulation to detect surface plasmon resonance. It can be used to determine the concentrations of bio-chemical materials in a sample. Its application includes the following detections, such as determining the concentrations of a medicine, characterizing affinity of a medicine with human serum albumin, monitoring chemicals and environmental pollution, and elsewhere.
2. Description of the Prior Art
Free charges in metal can be driven to move back and forth by an alternating electromagnetic field. The driven changing charge density leads to the so-called plasma oscillation. An electromagnetic wave incident on the metal can couple with the plasmon oscillation to produce the surface plasmon resonance, provided that proper conditions related with the polarization and the wavelength of the incident electromagnetic field are fulfilled. The resonance conditions relate to the conservation of energy and momentum in the system involving the exciting photons and the excited surface plasmons. Since the resonance conditions depend on the dielectric constants of the two materials on two sides of the metal, monitoring the dependence of the energy loss of the electromagnetic wave on the wavelength can be used to determine the dielectric constants. Specifically, the wavelength corresponding to the maximum energy loss is the surface-plasmon-resonance wavelength and can be used to determine the dielectric constants.
The surface plasmon resonance phenomenon as described above is taken as a characterization principle in a surface-plasmon-resonance sensing device, which is usually applied in characterization systems for biological and bio-chemical purposes. This kind of surface plasmon resonance device has the following advantages, such as real-time and/or specific analyzing without a labeling step, high sensitivity, and high throughput screening. Application of this technique can provides real-time characterization of the changes of a sample with the time. Its application fields include the characterization of various chemical gases or solutions, the monitoring of pollution, and the chip design for biological purposes. Furthermore, the integrated-optic version of surface plasmon resonance sensing device exhibits advantages of a solid structure, a small volume, a high sensitivity and portability. It can be further integrated with other integrated-optic devices on a single chip to form an integrated-optic circuit with a variety of functions.
For detecting the dependence of the surface plasmon resonance phenomena on the changes of a sample's properties, a spectrometer is needed in a conventional integrated-optic sensing device based on surface plasmon resonance. The sensitivity of the characterization is limited to the resolution of the spectrometer. For preventing from errors resulting from the vibration of the spectrometer, a vibration isolator for installing the spectrometer is needed. Because of using the spectrometer, the cost for building the characterization system is high. Besides, due to the huge volume of the overall system, its application is limited to laboratory work and not suitable for outdoor real-time sensing.